Download Water Engineering Exam for Structural Engineering Students at Cork Institute of Technology and more Exams Structures and Materials in PDF only on Docsity!
Cork Institute of Technology
Bachelor of Engineering (Honours) in Structural Engineering – Stage 3
(NFQ – Level 8)
Summer 2007
Water Engineering
(Time: 3 Hours)
Instructions Answer five questions in total, a minimum of Two questions from each section. Use separate answer books for each section. All questions carry equal marks. Programmable calculators are not permitted.
Examiners: Dr. J Harrington Mr. L O’Driscoll Prof. P. O’Donoghue Mr. P. Anthony
SECTION A
Note: Attachments including equations
1(a) A rectangular channel of width 1m and slope of 2 in 1000 conveys water at a rate of 3 m^3 /sec. Determine the depth of uniform flow for a Chezy Coefficient of 56. Determine the flow classification. What is the equivalent Manning roughness coefficient? (10 marks)
1(b) A channel of rectangular cross-section 12m wide with a slope of 1 in 2000 has a water depth of 3.5m. The Manning roughness coefficient is 0.025. A dam is built downstream. If the depth of water at the dam is 6m, find how far upstream it will be 4.5m. (10 marks)
2(a) Briefly discuss: (i) River water level measurement (5 marks) (ii) Dilution method of river flow measurement (5 marks)
2(b) Use the Muskingum Flood Routing Equation to find the peak outflow within a river reach for the following inflow hydrograph.
Day Time Inflow (m 3 /sec) 1 Midnight 1. 2 Noon 1. Midnight 3. 3 Noon 8. Midnight 13. 4 Noon 18. Midnight 19. 5 Noon 18. Midnight 16. 6 Noon 11. Midnight 8. 7 Noon 5. Midnight 5. 8 Noon 4. Midnight 3.
It may be assumed that X = 0.25 and K = 27 hours. Plot the appropriate inflow and outflow hydrographs. Comment on these results. (10 marks)
3(a) Discuss the following: (i) Types of River Water Pollution (3 marks) (ii) Wastewater Reuse and Recycling (3 marks) (iii) Desalination (2 marks)
3(b) Determine the minimum capacity of a storage reservoir required to maintain a constant water supply for a population equivalent of 400,000 given the following monthly mean inflow values (inflow x 10 6 m^3 /month):
Month 1 2 3 4 5 6 7 8 9 10 11 12 Inflow (x 10^6 ) 10 11.3 6.4 5.1 2.7 1.3 0.9 1.2 2.1 2.9 5.0 8.
Check your answer using an alternative method. In reality, what limitations are associated with this type of storage analysis? (12 mark 4(a) Discuss in detail the water treatment practiced at the Inniscarra Water Treatment Plant including a line diagram of the treatment process. (^) (14 marks)
SECTION B
QB1 A storm-water sewer is shown in Figure B1. The lengths of the pipes and the catchments are shown. Assume the ground falls uniformly from manhole to manhole. Allow for 1.2m between cover level, (CL), and top of pipe. Invert Level, (IL) = CL – 1.2m – diameter of pipe. Assume Time of entry of 4 minutes. For each pipe calculate the time of flow from header manhole and add to time of entry, round this value up to nearest ½ minute. Use the Dillon equation to establish rain intensity, I = 152.4 T (^) p 0.2^ / t 0. I is rain intensity in mm/hr, T (^) p is the return period and t is the storm duration in minutes. Use the Modified Rational method to establish flow, (^) Q = 2.78 Cv.C (^) r .I. A Q is the flow in L/s, I is rain intensity in mm/hr and A is the impermeable area in Ha. PR = 80%; Cr = 1.
Design the sewer in Figure B1, for a return period of 5 years. Indicate the pipe diameters & pipe slopes using the attached Table B1. Indicate the upstream and downstream invert levels for each pipe. Minimum and maximum velocities are 0.5m/s and 3 m/s respectively. Attachments B1: Colebrook White Chart with K (^) s = 0.6 and pipe design sheet. (20 marks)
Figure B
MH GL 80.00mOD Area 1 ha
MH GL 79.00mOD Area 0.8 ha
MH GL 79.50mOD Area 0.8 ha
MH GL 79.00mOD Area 0.5 ha
MH GL 78.50mOD Area 0ha
MH GL 79.50mOD 0.5 ha Pipe 1.
Pipe 1.
Pipe 1.
Pipe 1.
Pipe 1.
Cork Institute of Technology
Table B1PipeNr
Pipelength(m)
Fall(m)
Slope(m/m)
Diamete
r (mm)
Velocit
y (m/s)
Timeof Entry(mins)
Timeof Flow(mins)
Timeof Conc(mins)
ImpArea(ha)
TotalImpArea(ha)
Rain(mm/hr)
Q (L/s)
Capacit
y (L/s)
Requireddiameter(mm)
UpstreamIL (mOD)
D/stream
IL (mOD)
70
60
50
60
40
- OD = 0.75 Q (BOD (^) i – BOD (^) e) + 2Va .MLSS (3 marks) Where OD is oxygen demand g/h Q is flow through plant m^3 /h BODi and BODe are the influent and effluent BOD levels in mg/L V (^) a is the volume of the basin in m^3 MLSS is the concentration of mixed liquor suspended solids in g/L
Figure B2 F/M ratio graph
QB3 In a sewerage scheme for a town of 30,000 person equivalents, (PE), a pump station is employed to convey the wastewater to the treatment works by rising main. The static lift is 35m and the length of rising main is 1700m. Three dry weather flows, (3DWF), are pumped forward. The wastewater conveyed to the pump station is from a separate foul sewer. (a) Size the pumps for each of the rising mains listed below. (5 marks) (b) Calculate the annualised cost of each option. Establish which is the most economic rising main. (13 marks) (c) What is the cost per house per annum of your recommended design assuming 3PE/house? (2 marks)
Available rising main diameter: 450mm or 525mm Assumptions: 1 PE = 220L/day ks = 1. Pump Power required = {Q(m^3 /hr) x H (m)}/125 kW Ignore standby pumps in economic analysis. Allow for 0.5m of station loss. Capital Costs: Rising main: 450 mm diameter = €300/m; 525 mm diameter = €350/m Pumps: 100kW - €80 000; 50 kW - €50 000; 30 kW - €40 000; 5 kW - €10 000. Pump Station: 80 % of capital cost of pumps Running Costs: Cost of Capital: R = P{(1+r) Nr}/{(1+r) N^ - 1} Where: P is the capitalised amount of annual payments R with return on investment r over N years. Use 5% return on investment over 10 years Running costs = 7% of capital cost of pumps. Cost of electricity = €0.1/kWh Attachments: Colebrook White Chart with ks = 1.
